Yes, it is illegal to grow poppies in Japan. The opium poppy, which is the plant that produces opium from which drugs such as morphine and heroin are derived, is classified as a narcotic in Japan under the Opium Law. Therefore, cultivating the opium poppy without a license is illegal and can result in severe penalties. It is also illegal to possess, use, or distribute opium or any other narcotic derived from the poppy plant in Japan. However, it is important to note that poppy seeds themselves are not illegal in Japan and can be found in some foods and baked goods.